The invention relates generally to the commercial and industrial refrigeration art, and more particularly to improvements in low head pressure surge-type receivers for refrigeration systems.
In the past, closed refrigeration systems having a single compressor or plural compressors have been used in commercial installations, such as supermarkets having a large number of low and/or normal temperature refrigerated fixtures or units for the display and storage of food products, or for industrial installations such as warehousing, lockers, manufacturing plants and the like having varying refrigeration requirements.
Hot gas defrosting in such systems is effective due to the large latent heat load produced by the refrigerated units in excess of the heat required for defrosting selected evaporator coils during the continued refrigeration of the remaining fixtures. However, highly superheated hot gas from the compressor for defrosting purposes has resulted in breakage and leaks caused by rapid thermal expansion of refrigerant lines, and the fog or vapor caused by high defrost temperatures frequently is visual in the refrigerated fixture or zone and may result in frost buildup on products. U.S. Pat. No. 3,343,375 teaches that the adverse effects of prior hot gas defrosting can be obviated by using saturated gas taken from the receiver or otherwise being desuperheated. It is also generally known in the refrigeration industry that subcooled liquid refrigerant from the condenser is advantageous in the operation of the evaporators and that low compressor head pressures result in substantial energy savings, and surge receiver systems to obtain these benefits, as well as utilize saturated gas defrost, are disclosed in U.S. Pat. Nos. 3,358,469; 3,427,819 and 4,522,037.
Refrigeration system operations throughout the year are directly affected by various climatic conditions. For instance, during winter operations the maintenance of proper compressor head pressures in the high side of the system has been a principal problem, particularly in recent years in which heat reclamation condensers have come into wide-spread usage; and during summer operations in which the machine room temperature was frequently below the condensing temperature of a roof-mounted or outside condenser, the supply of saturated gas for defrosting was severely limited or substantially non-existent due to its condensation to liquid form and overfill "lugging" of the receiver.
In short, prior systems having either flow-through or surge receivers and utilizing saturated gas defrost and winter heat reclamation condensers have had various high side control problems throughout the various climatic seasonal changes and effects on such systems and, while various control arrangements have been proposed, year-round system operations have not been efficiently controlled heretofore.